From: "Yan, Zheng" <zheng.z....@intel.com>
When the LBR call stack is enabled, it is necessary to save/restore
the LBR stack on context switch. The solution is saving/restoring
the LBR stack to/from task's perf event context.
Signed-off-by: Yan, Zheng <zheng.z....@intel.com>
---
arch/x86/kernel/cpu/perf_event.c | 1 +
arch/x86/kernel/cpu/perf_event.h | 8 +++
arch/x86/kernel/cpu/perf_event_intel_lbr.c | 101 ++++++++++++++++++++++++-----
include/linux/perf_event.h | 5 ++
kernel/events/core.c | 22 ++++++-
5 files changed, 121 insertions(+), 16 deletions(-)
diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index b96aea8..d29d852 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -1879,6 +1879,7 @@ static struct pmu pmu = {
.event_idx = x86_pmu_event_idx,
.sched_task = x86_pmu_sched_task,
+ .task_ctx_size = sizeof(struct x86_perf_task_context),
};
void arch_perf_update_userpage(struct perf_event_mmap_page *userpg, u64 now)
diff --git a/arch/x86/kernel/cpu/perf_event.h b/arch/x86/kernel/cpu/perf_event.h
index 62f6ee8..b1d2fa9 100644
--- a/arch/x86/kernel/cpu/perf_event.h
+++ b/arch/x86/kernel/cpu/perf_event.h
@@ -150,6 +150,7 @@ struct cpu_hw_events {
* Intel LBR bits
*/
int lbr_users;
+ int lbr_sys_users;
struct perf_branch_stack lbr_stack;
struct perf_branch_entry lbr_entries[MAX_LBR_ENTRIES];
struct er_account *lbr_sel;
@@ -458,6 +459,13 @@ struct x86_pmu {
struct perf_guest_switch_msr *(*guest_get_msrs)(int *nr);
};
+struct x86_perf_task_context {
+ u64 lbr_from[MAX_LBR_ENTRIES];
+ u64 lbr_to[MAX_LBR_ENTRIES];
+ int lbr_callstack_users;
+ bool lbr_stack_saved;
+};
+
enum {
PERF_SAMPLE_BRANCH_CALL_STACK_SHIFT = PERF_SAMPLE_BRANCH_MAX_SHIFT,
PERF_SAMPLE_BRANCH_SELECT_MAP_SIZE,
diff --git a/arch/x86/kernel/cpu/perf_event_intel_lbr.c
b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
index 468ac1d..a160891 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_lbr.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
@@ -187,29 +187,103 @@ void intel_pmu_lbr_reset(void)
intel_pmu_lbr_reset_64();
}
+/*
+ * TOS = most recently recorded branch
+ */
+static inline u64 intel_pmu_lbr_tos(void)
+{
+ u64 tos;
+
+ rdmsrl(x86_pmu.lbr_tos, tos);
+
+ return tos;
+}
+
+static void __intel_pmu_lbr_restore(struct x86_perf_task_context *task_ctx)
+{
+ int i;
+ unsigned lbr_idx, mask = x86_pmu.lbr_nr - 1;
+ u64 tos = intel_pmu_lbr_tos();
+
+ for (i = 0; i < x86_pmu.lbr_nr; i++) {
+ lbr_idx = (tos - i) & mask;
+ wrmsrl(x86_pmu.lbr_from + lbr_idx, task_ctx->lbr_from[i]);
+ wrmsrl(x86_pmu.lbr_to + lbr_idx, task_ctx->lbr_to[i]);
+ }
+ task_ctx->lbr_stack_saved = false;
+}
+
+static void __intel_pmu_lbr_save(struct x86_perf_task_context *task_ctx)
+{
+ int i;
+ unsigned lbr_idx, mask = x86_pmu.lbr_nr - 1;
+ u64 tos = intel_pmu_lbr_tos();
+
+ for (i = 0; i < x86_pmu.lbr_nr; i++) {
+ lbr_idx = (tos - i) & mask;
+ rdmsrl(x86_pmu.lbr_from + lbr_idx, task_ctx->lbr_from[i]);
+ rdmsrl(x86_pmu.lbr_to + lbr_idx, task_ctx->lbr_to[i]);
+ }
+ task_ctx->lbr_stack_saved = true;
+}
+
+
void intel_pmu_lbr_sched_task(struct perf_event_context *ctx, bool sched_in)
{
+ struct cpu_hw_events *cpuc;
+ struct x86_perf_task_context *task_ctx;
+
if (!x86_pmu.lbr_nr)
return;
+
+ cpuc = &__get_cpu_var(cpu_hw_events);
+ task_ctx = ctx ? ctx->task_ctx_data : NULL;
+
/*
* It is necessary to flush the stack on context switch. This happens
* when the branch stack does not tag its entries with the pid of the
* current task.
*/
- if (sched_in)
- intel_pmu_lbr_reset();
+ if (sched_in) {
+ if (cpuc->lbr_sys_users > 0 ||
+ !task_ctx ||
+ !task_ctx->lbr_stack_saved ||
+ !task_ctx->lbr_callstack_users)
+ intel_pmu_lbr_reset();
+ else
+ __intel_pmu_lbr_restore(task_ctx);
+ } else if (task_ctx) {
+ if (task_ctx->lbr_callstack_users)
+ __intel_pmu_lbr_save(task_ctx);
+ else
+ task_ctx->lbr_stack_saved = false;
+ }
+}
+
+static inline bool branch_user_callstack(unsigned br_sel)
+{
+ return (br_sel & X86_BR_USER) && (br_sel & X86_BR_CALL_STACK);
}
void intel_pmu_lbr_enable(struct perf_event *event)
{
struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
+ struct x86_perf_task_context *task_ctx;
if (!x86_pmu.lbr_nr)
return;
+ cpuc = &__get_cpu_var(cpu_hw_events);
+ task_ctx = event->ctx ? event->ctx->task_ctx_data : NULL;
+
cpuc->br_sel = event->hw.branch_reg.reg;
+ if (!(event->attach_state & PERF_ATTACH_TASK))
+ cpuc->lbr_sys_users++;
+ else if (branch_user_callstack(cpuc->br_sel))
+ task_ctx->lbr_callstack_users++;
+
cpuc->lbr_users++;
if (cpuc->lbr_users == 1)
perf_sched_cb_enable(event->ctx->pmu);
@@ -217,10 +291,19 @@ void intel_pmu_lbr_enable(struct perf_event *event)
void intel_pmu_lbr_disable(struct perf_event *event)
{
- struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
+ struct cpu_hw_events *cpuc;
+ struct x86_perf_task_context *task_ctx;
if (!x86_pmu.lbr_nr)
return;
+
+ cpuc = &__get_cpu_var(cpu_hw_events);
+ task_ctx = event->ctx ? event->ctx->task_ctx_data : NULL;
+
+ if (!(event->attach_state & PERF_ATTACH_TASK))
+ cpuc->lbr_sys_users--;
+ else if (branch_user_callstack(cpuc->br_sel))
+ task_ctx->lbr_callstack_users--;
cpuc->lbr_users--;
WARN_ON_ONCE(cpuc->lbr_users < 0);
@@ -248,18 +331,6 @@ void intel_pmu_lbr_disable_all(void)
__intel_pmu_lbr_disable();
}
-/*
- * TOS = most recently recorded branch
- */
-static inline u64 intel_pmu_lbr_tos(void)
-{
- u64 tos;
-
- rdmsrl(x86_pmu.lbr_tos, tos);
-
- return tos;
-}
-
static void intel_pmu_lbr_read_32(struct cpu_hw_events *cpuc)
{
unsigned long mask = x86_pmu.lbr_nr - 1;
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 991bcf5..23471c2 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -252,6 +252,10 @@ struct pmu {
*/
void (*sched_task) (struct perf_event_context *ctx,
bool sched_in); /*optional */
+ /*
+ * PMU specific data size
+ */
+ size_t task_ctx_size;
};
/**
@@ -471,6 +475,7 @@ struct perf_event_context {
int pin_count;
int nr_cgroups; /* cgroup evts */
int nr_branch_stack; /* branch_stack evt */
+ void *task_ctx_data; /* pmu specific data */
struct rcu_head rcu_head;
};
diff --git a/kernel/events/core.c b/kernel/events/core.c
index a6e11fd..89ce4f9 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -882,6 +882,16 @@ static void get_ctx(struct perf_event_context *ctx)
WARN_ON(!atomic_inc_not_zero(&ctx->refcount));
}
+static void free_ctx(struct rcu_head *head)
+{
+ struct perf_event_context *ctx;
+
+ ctx = container_of(head, struct perf_event_context, rcu_head);
+ if (ctx->task_ctx_data)
+ kfree(ctx->task_ctx_data);
+ kfree(ctx);
+}
+
static void put_ctx(struct perf_event_context *ctx)
{
if (atomic_dec_and_test(&ctx->refcount)) {
@@ -889,7 +899,7 @@ static void put_ctx(struct perf_event_context *ctx)
put_ctx(ctx->parent_ctx);
if (ctx->task)
put_task_struct(ctx->task);
- kfree_rcu(ctx, rcu_head);
+ call_rcu(&ctx->rcu_head, free_ctx);
}
}
@@ -2280,6 +2290,8 @@ static void perf_event_context_sched_out(struct
task_struct *task, int ctxn,
next->perf_event_ctxp[ctxn] = ctx;
ctx->task = next;
next_ctx->task = task;
+ ctx->task_ctx_data = xchg(&next_ctx->task_ctx_data,
+ ctx->task_ctx_data);
do_switch = 0;
perf_event_sync_stat(ctx, next_ctx);
@@ -2994,6 +3006,14 @@ alloc_perf_context(struct pmu *pmu, struct task_struct
*task)
if (!ctx)
return NULL;
+ if (pmu->task_ctx_size) {
+ ctx->task_ctx_data = kzalloc(pmu->task_ctx_size, GFP_KERNEL);
+ if (!ctx->task_ctx_data) {
+ kfree(ctx);
+ return NULL;
+ }
+ }
+
__perf_event_init_context(ctx);
if (task) {
ctx->task = task;
--
1.8.1.4
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